Carbon nanotubes (CNTs) have a 1D cylindrical build with micrometer-scale length and diameters of nanometer-scale [1]. The structure is an empty cylindrical that is caused by the movement of single or multiple substrates of graphene slabs. Depending on the nature of the external layer or wall CNTs are mainly of two original types: SWCNTs (single-walled carbon) [2] and MWCNTs (multi-walled carbon nanotubes) [1,3,4]. Fig. 1 shows the interior see and the surface of a SWCNT. The phrase SWCNTs was first defined in 1993 [2,5]. SWCNTs are a single substrate of graphene sheet diameter 1–2 nm. Double-walled carbon nanotubes (DWCNTs) can be considered a specific type of CNTs because of morphology and virtues similar to SWCNTs (Fig. 1). Also, DWCNTs are more resistant to the somewhat rough chemical stages required to become functionalized; therefore, they have more chemically constant [5]. DWCNTs are composed of two CNTs that are distinct where the external pipe surrounds the internal pipe. The internal pipe diameter is 1–3 nm and the external pipe diameter is 2–4 nm [1]. Iijima first found MWCNTs and their procurement is based incidence of hard sediments on the cathode utilizing arc vaporization [6,7]. MWCNTs are also named and numbered depending on the graphene plates and the diameters span between 2 and 200 nm [5,8]. MWCNTs have 2 structural types the Parchment model and the Russian doll. In the model of the alternative Parchment, twisting a sheet of graphene around itself several times causes the paper scroll to rotate. The model of the Russian doll is a graphene sheet arrangement in cylinders of concentric [9].

The CNTs have specific traits such as thermal traits, electrical, chemical, and mechanical that have been widely studied for use in applied usages. For example, biosensors technology, and application in pharmaceutical and clinical have been considerable [10,11]. Biosensors have garnered significant interest in the biotechnology sector because of their extraordinary qualities, such as amazing sensitivity, simplicity of installation, and rapid response times. They have been widely used for the identification of diverse target analytes, such as antigens, viruses, and biomarkers linked to various illnesses [12,13]. This review presents an introduction to the idea of biosensors and discusses the many varieties, including CNT biosensors. It also explores the use of these biosensors in the detection of different illnesses on different biosensor platforms. Lastly, it emphasizes crucial clinical criteria such as the range of detection, the limit of detection (LOD), and the design of the bioassay.